Method and system for the heat-pump control to reduce liquid refrigerant migration

ABSTRACT

A method of mitigating liquid-refrigerant migration includes comparing a requested compressor speed of a variable-speed compressor to a pre-defined threshold and, responsive to a determination that the requested compressor speed is greater than the pre-defined threshold, operating the variable-speed compressor at a first compressor speed that is less than the requested compressor speed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/102,660, filed on Nov. 24, 2020. U.S. patent application Ser. No.17/102,660 is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to heating, ventilation, andair conditioning (HVAC) systems and more particularly, but not by way oflimitation, to heat-pump control to reduce liquid-refrigerant migration.

BACKGROUND

This section provides background information to facilitate a betterunderstanding of the various aspects of the disclosure. It should beunderstood that the statements in this section of this document are tobe read in this light, and not as admissions of prior art.

Vapor-compression systems are used to regulate environmental conditionswithin an enclosed space. Typically, such systems have a circulation fanthat pulls air from the enclosed space through ducts and pushes the airback into the enclosed space through additional ducts after conditioningthe air (e.g., heating or cooling). To direct operation of thecirculation fan and other components, such systems include a controller.In addition to directing operation of the system, the controller may beused to monitor various components of the system to determine if thecomponents are functioning properly.

In vapor-compression systems, a refrigerant undergoes phase changes.During operation of such systems, refrigerant can migrate into a systemcompressor when, for example, an operating mode of the system is changedfrom a defrost mode to a heating mode. This is undesirable. During adefrost cycle, liquid refrigerant can accumulate in an outdoor coil ofthe vapor-compression system. When the defrost cycle has completed andoperation of the system in the heating mode is initiated, liquidrefrigerant stored in the outdoor coil can migrate into an accumulatorand eventually into a compressor chamber, which migration can causedamage to the compressor. Liquid migration can also wash out compressorlubricant, which can lead to overheating of the compressor and eventualcompressor failure. Sometimes use of the accumulator is a satisfactorymitigation of the problem of liquid-refrigerant migration; however, evenwhen the accumulator is utilized, liquid-refrigerant migration sometimesstill occurs.

SUMMARY

This summary is provided to introduce a selection of concepts that arefurther described below in the detailed description. This summary is notnecessarily intended to identify key or essential features of theclaimed subject matter, nor is it intended to be used as an aid inlimiting the scope of claimed subject matter.

A method of mitigating liquid-refrigerant migration includes comparing arequested compressor speed of a variable-speed compressor to apre-defined threshold and, responsive to a determination that therequested compressor speed is greater than the pre-defined threshold,operating the variable-speed compressor at a first compressor speed thatis less than the requested compressor speed.

A computer-program product includes a non-transitory computer-usablemedium having computer-readable program code embodied therein. Thecomputer-readable program code is adapted to be executed to implement amethod. The method includes comparing a requested compressor speed of avariable-speed compressor to a pre-defined threshold and, responsive toa determination that the requested compressor speed is greater than thepre-defined threshold, operating the variable-speed compressor at afirst compressor speed that is less than the requested compressor speed.

An information handling system includes a processor. The processor isoperable to implement a method. The method includes comparing arequested compressor speed of a variable-speed compressor to apre-defined threshold and, responsive to a determination that therequested compressor speed is greater than the pre-defined threshold,operating the variable-speed compressor at a first compressor speed thatis less than the requested compressor speed.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with standard practice in the industry, variousfeatures are not drawn to scale. In fact, the dimensions of variousfeatures may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a block diagram of an illustrative vapor-compression system;

FIG. 2 is a flow diagram that illustrates a method of control to reduceliquid-refrigerant migration; and

FIG. 3 is a flow diagram that illustrates another method of control toreduce liquid-refrigerant migration.

DETAILED DESCRIPTION

Various embodiments will now be described more fully with reference tothe accompanying drawings. The disclosure may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein.

FIG. 1 is a schematic diagram of an illustrative vapor-compressionsystem 100. The vapor-compression system may operate in a heating modeor in a defrost mode. The vapor-compression system 100 includes avariable-speed compressor 102, an accumulator 104, a reversing valve106, a condenser 108, an expansion device 110, a condenser fan 112, anexpansion device 114, an evaporator 116, an evaporator fan 118, and acontroller 122. What is referred to as an outdoor unit 120 includes thevariable-speed compressor 102, the accumulator 104, the reversing valve106, the expansion device 114, the evaporator 116, and the evaporatorfan 118. The condenser 108, the expansion device 110, and the condenserfan 112 are located inside an enclosed space to be heated. In a typicalembodiment, each of the expansion devices 110 and 114 may be, forexample, a thermostatic expansion valve or a throttling valve. Thevapor-compression system 100 is controlled via the controller 122.

When the vapor-compression system 100 is operating in the heating mode,refrigerant leaves the variable-speed compressor 102 as ahigh-temperature high-pressure vapor and passes to the reversing valve106. The reversing valve 106 is positioned in the heating mode so therefrigerant passes through the reversing valve 106 and is directed tothe condenser 108 which, as noted above, is located inside the enclosedspace to be heated. Cool air is blown by the condenser fan 112 over thecondenser 108 inside the enclosed space to remove some of the thermalenergy from the refrigerant and provide heating to the enclosed space.As heat is removed from the refrigerant, the refrigerant condenses intoa liquid. Having given up some of its energy to provide heat to theenclosed space, the refrigerant leaves the condenser 108 as ahigh-pressure slightly cooler liquid.

The refrigerant is directed from the condenser 108 to the expansiondevice 110 and then to the expansion device 114. Because thevapor-compression system 100 is in the heating mode, the expansiondevice 110 is closed such the liquid refrigerant passes through theexpansion device 110 and is directed to the expansion device 114. Therefrigerant passes through the expansion device 114, where therefrigerant expands in volume and turns into a part-liquid part-vapormixture. This expansion of the refrigerant by the expansion device 114reduces the temperature and pressure of the refrigerant. As therefrigerant exits the expansion device 114, the refrigerant is alow-pressure low-temperature liquid/vapor mixture.

From the expansion device 114, the refrigerant is directed to theevaporator 116. The evaporator fan 118 blows outside ambient air overcoils of the evaporator 116, which serves to add heat to therefrigerant. Because the refrigerant boils at a very low temperature, asit boils, thermal energy imparted to the refrigerant from the outsideambient air is carried away. Thermal energy is picked up by therefrigerant from the outside ambient air and the refrigerant leaves theevaporator 116 as a low-pressure low-temperature slightly superheatedvapor and is directed to the reversing valve 106. The reversing valve106 diverts the refrigerant to the accumulator 104. From the accumulator104, the refrigerant returns to the variable-speed compressor 102.

If the vapor-compression system 100 is then switched into the defrostmode, the variable-speed compressor 102 forces the high-pressure hightemperature vapor refrigerant into the reversing valve 106. Thereversing valve 106 diverts this high-pressure high-temperature vaporrefrigerant to the evaporator 116, which in the defrost mode operates asa condenser. The evaporator fan 118 is turned off in order to increasethe temperature of the refrigerant in the coil of the evaporator 116 inorder to melt frost on the coil of the evaporator 116. Since therefrigerant is at a warmer temperature than the surrounding air, thermalenergy of the refrigerant is carried away. The refrigerant condenses asit loses thermal energy and leaves the evaporator 116 as a high-pressurelower temperature liquid.

From the evaporator 116, the refrigerant is directed to the expansiondevice 114, which is closed, so the refrigerant passes through expansiondevice 114 to expansion device 110. As the refrigerant passes throughthe expansion device 110, the refrigerant changes to a part-liquidpart-vapor mixture due to a drop in pressure and temperature andtemperature of the refrigerant. From the expansion device 110, therefrigerant flows into the condenser 108. At the condenser 108, whichoperates in the defrost mode as an evaporator, the condenser fan 112blows warm indoor air over the coil of the condenser 108, which causesheat from inside the enclosed space to transfer from the inside air tothe refrigerant; as a result, the refrigerant boils and takes heat away.The refrigerant leaves the condenser 108 in a low-pressurelow-temperature slightly superheated state and flows into the reversingvalve 106. The reversing valve 106 diverts the refrigerant back to theaccumulator 104. From the accumulator 104, the refrigerant returns tothe variable-speed compressor 102.

The function of the accumulator 104 is to store liquid refrigerant. Insome circumstances, the liquid refrigerant will exit the evaporator 116and reach the accumulator 104 via the reversing valve 106. In somecases, use of the accumulator 104 is a satisfactory mitigation of theproblem of liquid refrigerant migration into the variable-speedcompressor 102. However, in other cases, even when the accumulator 104is present and operating properly, liquid refrigerant migration to thevariable-speed compressor 102 can still occur. In such cases, liquidrefrigerant migration can be managed by controlling operation of thevariable-speed compressor 102 after, for example, defrost-modetermination, as described in more detail below.

In a typical refrigerant-liquid mitigation method, when a defrost cycleis terminated, the variable-speed compressor 102 is shut off to allowthe reversing valve 106 to switch to the heating mode. Much of theliquid refrigerant is stored in the evaporator 116 when the defrostcycle is completed. When the heating mode is initiated, thevariable-speed compressor 102 often runs at high speed due to highheating demand. In such a case, it is possible for foaming, due to oiland refrigerant mix, to occur in the accumulator 104 for as long as 3-5minutes. When oil solubility is high enough, foaming can occur whenliquid refrigerant is evaporated from a mixture of oil and liquidrefrigerant during restart of the vapor-compression system 100.Prolonged foaming can cause lubricant in the variable-speed compressor102 to be pumped out from the variable-speed compressor 102 andeventually lead to failure of the variable-speed compressor 102.

A typical embodiment of the accumulator 104 includes a J-shaped tube,including an opening on a hook portion of the J-shaped tube whererefrigerant vapor can enter. The vapor refrigerant goes down and up astem portion of the J-tube of the accumulator 104 and from theaccumulator 104 is directed to the variable-speed compressor 102. As therefrigerant, in a liquid and vapor form, enters the accumulator 104, aliquid portion of the refrigerant falls to the bottom of the accumulator104 and eventually evaporates into a vapor. The vapor is pulled into theJ-tube and is directed to the variable-speed compressor 102. Thus, theaccumulator 104 is designed to prevent liquid refrigerant from reachingthe variable-speed compressor 102.

However, if, for example, the expansion device 114 is not operatingproperly and is flooding, damage to the variable-speed compressor 102can result if the accumulator 104 cannot adequately compensate. Floodingcan occur when the expansion device 114 feeds the evaporator 116 withtoo much of the refrigerant (i.e., more refrigerant than the evaporator116 can evaporate), such that the variable-speed compressor 102 caneventually be damaged as the liquid refrigerant reaches thevariable-speed compressor 102.

In addition, when the vapor-compression system 100 is in an off cyclesuch that the vapor-compression system 100 is not running and theoutside ambient temperature is cooler than inside the enclosed space, inwhich case liquid refrigerant tends to accumulate in the evaporator 116,liquid refrigerant can collect inside the accumulator 104.

Moreover, undesirable effects can occur when the vapor-compressionsystem 100 is operating in a defrost cycle. At the end of a defrostcycle, the reversing valve 106 shifts. Since the evaporator 116 acts asa condenser when the vapor-compression system 100 is in defrost mode,the evaporator 116 has liquid refrigerant in its coil. As a result, whenthe vapor-compression system 100 shifts from the defrost mode into theheating mode, liquid refrigerant that has accumulated in the evaporator116 is directed to the accumulator 104 via the reversing valve 106.

FIG. 2 is a flow diagram that illustrates a method of control to reduceliquid-refrigerant migration. A flow 200 as illustrated may be utilizedin the operation of a system such as, for example, the vapor-compressionsystem 100. Principles outlined herein relative to the flow 200 couldalso be employed in systems other than the illustrated vapor-compressionsystem 100 such as a cooling-only system.

The flow 200 begins at step 202. At step 202, heating demand or the endof a defrost call occur. In other words, there is a need for the systemto operate in the heating mode or the system discontinues operation inthe defrost mode. From step 202, execution proceeds to step 204. At step204, an Operation Hold Off Timer (“OHT”) is set to zero. From step 204,execution proceeds to step 206, at which step the OHT is incremented.

From step 206, execution proceeds to step 208. At step 208, adetermination is made as to whether the heating demand necessitatescompressor operation at greater than 50 Hz. Those having skill in theart will appreciate that compressor operation frequency is greater inresponse to greater heating demand and is less in response to lowerheating demand.

In response to a positive determination at step 208, execution proceedsto step 210. At step 210, if the OHT is less than 1 minute, executionproceeds to step 216. If, at step 210 the OHT is not less than 1 minute,execution proceeds to step 212.

At step 208, if the heating demand is not greater than 50 Hz, executionproceeds to step 214. At step 214, the system operates at the speedmandated by the heating demand. At step 210, if the OHT is less than 1minute, execution proceeds to step 216, at which that the systemoperates at 30 Hz.

At step 212, if the OHT is less than 2 minutes, execution proceeds tostep 218, at which step the system operates at 40 Hz. At step 212, ifthe OHT is not less than 2 minutes, execution proceeds to step 220, atwhich step the system operates at 50 Hz.

From step 214, execution proceeds to step 222, at which step adetermination is made as to whether the OHT is greater than or equal to3 minutes. If the determination at step 222 is positive, executionproceeds to step 224, at which step other operations are resumed. If, atstep 222, the determination is negative, execution returns from step 222to step 208. From each of steps 216, 218, and 220, execution proceeds tostep 222.

Although the flow 200 utilizes particular frequencies and timer periods,as well as a particular number of steps between different frequencies,those having skill in the art will appreciate that differentfrequencies, time or periods, and number of steps between differentfrequencies may be utilized in accordance with design considerationswithout departing from the principles set forth in this disclosure.

It is thus apparent that the flow 200 allows the frequency of operationof the system to be ramped up in a stepwise fashion in order to limitliquid refrigerant flow and thereby avoid overwhelming the accumulatorwith too much liquid refrigerant. As such, the accumulator can betterevaporate liquid refrigerant so that liquid-refrigerant migration intothe compressor can be avoided or minimized. This is particularly truewhen heating demand is high and consequent compressor frequencies aregreat upon initiation of heating demand or the end of a defrost call.

FIG. 3 is a flow diagram that illustrates a method of control to reduceliquid-refrigerant. A flow 300 as illustrated may be utilized in theoperation of a system such as, for example, the vapor-compression system100. Principles outlined herein relative to the flow 300 could also beemployed in cooling-only systems.

The flow 300 begins at step 302. At step 302, heating demand or the endof a defrost call occur. In other words, there is a need for the systemto operate in the heating mode or the system discontinues operation inthe defrost mode. From step 302, execution proceeds to step 304.

At step 304, an operation timer is set to zero. From step 304, executionproceeds to step 306, at which step a determination is made as towhether heating demand is greater than 50 Hz. In response to a positivedetermination at step 306, the system operates at 50 Hz. In response toa negative determination at step 306, the system operates at the heatingdemand speed.

From each of steps 308 and 310, execution proceeds to step 312. At step312, a determination is made as to whether greater than three minuteshave elapsed on the operation timer. In response to a positivedetermination at step 312, execution proceeds to step 314, at which stepnormal operation of the system is resumed. In response to a negativedetermination at step 312, execution returns to step 306.

Although the flow 300 utilizes particular frequencies and timer periods,as well as a particular number of steps between different frequencies,those having skill in the art will appreciate that differentfrequencies, time or periods, and number of steps between differentfrequencies may be utilized in accordance with design considerationswithout departing from the principles set forth in this disclosure.

It is thus apparent that the flow 300 allows the frequency of operationof the system to be ramped up in a stepwise fashion in order to limitrefrigerant flow and thereby avoid overwhelming the accumulator with toomuch liquid refrigerant. As such, the accumulator can better evaporateliquid refrigerant so that liquid-refrigerant migration into thecompressor can be avoided or minimized. This is particularly true whenheating demand is high and consequent compressor frequencies are greatupon initiation of heating demand or the end of a defrost call.

The term “substantially” is defined as largely but not necessarilywholly what is specified (and includes what is specified; e.g.,substantially 90 degrees includes 90 degrees and substantially parallelincludes parallel), as understood by a person of ordinary skill in theart. In any disclosed embodiment, the terms “substantially,”“approximately,” “generally,” and “about” may be substituted with“within 10% of” what is specified.

For purposes of this patent application, the term computer-readablestorage medium encompasses one or more tangible computer-readablestorage media possessing structures. As an example and not by way oflimitation, a computer-readable storage medium may include asemiconductor-based or other integrated circuit (IC) (such as, forexample, a field-programmable gate array (FPGA) or anapplication-specific IC (ASIC)), a hard disk, an HDD, a hybrid harddrive (HHD), an optical disc, an optical disc drive (ODD), amagneto-optical disc, a magneto-optical drive, a floppy disk, a floppydisk drive (FDD), magnetic tape, a holographic storage medium, asolid-state drive (SSD), a RAM-drive, a SECURE DIGITAL card, a SECUREDIGITAL drive, a flash memory card, a flash memory drive, or any othersuitable tangible computer-readable storage medium or a combination oftwo or more of these, where appropriate.

Particular embodiments may include one or more computer-readable storagemedia implementing any suitable storage. In particular embodiments, acomputer-readable storage medium implements one or more portions of acontroller as appropriate. In particular embodiments, acomputer-readable storage medium implements RAM or ROM. In particularembodiments, a computer-readable storage medium implements volatile orpersistent memory. In particular embodiments, one or morecomputer-readable storage media embody encoded software.

In this patent application, reference to encoded software may encompassone or more applications, bytecode, one or more computer programs, oneor more executables, one or more instructions, logic, machine code, oneor more scripts, or source code, and vice versa, where appropriate, thathave been stored or encoded in a computer-readable storage medium. Inparticular embodiments, encoded software includes one or moreapplication programming interfaces (APIs) stored or encoded in acomputer-readable storage medium. Particular embodiments may use anysuitable encoded software written or otherwise expressed in any suitableprogramming language or combination of programming languages stored orencoded in any suitable type or number of computer-readable storagemedia. In particular embodiments, encoded software may be expressed assource code or object code. In particular embodiments, encoded softwareis expressed in a higher-level programming language, such as, forexample, C, Python, Java, or a suitable extension thereof. In particularembodiments, encoded software is expressed in a lower-level programminglanguage, such as assembly language (or machine code). In particularembodiments, encoded software is expressed in JAVA. In particularembodiments, encoded software is expressed in Hyper Text Markup Language(HTML), Extensible Markup Language (XML), or other suitable markuplanguage.

Depending on the embodiment, certain acts, events, or functions of anyof the algorithms described herein can be performed in a differentsequence, can be added, merged, or left out altogether (e.g., not alldescribed acts or events are necessary for the practice of thealgorithms). Moreover, in certain embodiments, acts or events can beperformed concurrently, e.g., through multi-threaded processing,interrupt processing, or multiple processors or processor cores or onother parallel architectures, rather than sequentially. Although certaincomputer-implemented tasks are described as being performed by aparticular entity, other embodiments are possible in which these tasksare performed by a different entity.

Conditional language used herein, such as, among others, “can,” “might,”“may,” “e.g.,” and the like, unless specifically stated otherwise, orotherwise understood within the context as used, is generally intendedto convey that certain embodiments include, while other embodiments donot include, certain features, elements and/or states. Thus, suchconditional language is not generally intended to imply that features,elements and/or states are in any way required for one or moreembodiments or that one or more embodiments necessarily include logicfor deciding, with or without author input or prompting, whether thesefeatures, elements and/or states are included or are to be performed inany particular embodiment.

While the above detailed description has shown, described, and pointedout novel features as applied to various embodiments, it will beunderstood that various omissions, substitutions, and changes in theform and details of the devices or algorithms illustrated can be madewithout departing from the spirit of the disclosure. As will berecognized, the processes described herein can be embodied within a formthat does not provide all of the features and benefits set forth herein,as some features can be used or practiced separately from others. Thescope of protection is defined by the appended claims rather than by theforegoing description. All changes which come within the meaning andrange of equivalency of the claims are to be embraced within theirscope.

What is claimed is:
 1. A method of mitigating liquid-refrigerantmigration using a processor, the method comprising: receiving one of aheating-demand call and an end-defrost call; determining a requestedcompressor speed responsive to the receiving step; comparing a requestedcompressor speed of a variable-speed compressor to a pre-definedthreshold; responsive to a determination that the requested compressorspeed is not greater than the pre-defined threshold, operating thevariable-speed compressor at the requested compressor speed; wherein theoperating step is performed for a pre-defined time period; beforeexpiration of the pre-defined time period, the comparing step isrepeated; responsive to a determination at the repeated comparing stepthat the requested compressor speed is greater than the pre-definedthreshold, operating the variable-speed compressor at the firstcompressor speed that is less than the requested compressor speed; andresponsive to a determination at the repeated comparing step that therequested compressor speed is not greater than the pre-definedthreshold, operating the variable-speed compressor at the requestedcompressor speed.
 2. The method of claim 1, comprising, responsive to adetermination that the requested compressor speed is greater than thepre-defined threshold, operating the variable-speed compressor at afirst compressor speed that is less than the requested compressor speed.3. The method of claim 1, wherein the method is performed on a vapor-compression system.
 4. The method of claim 1, comprising: performing theoperating step for a first pre-defined time period; and after expirationof the first pre-defined time period, operating the variable-speedcompressor at a second compressor speed greater than the firstcompressor speed and less than the requested compressor speed.
 5. Themethod of claim 4, comprising: performing the step of operating thevariable-speed compressor at the second compressor speed for a secondpre-defined time period.
 6. The method of claim 5, comprising: afterexpiration of the second pre-defined time period, operating thevariable-speed compressor at a third compressor speed greater than thesecond compressor speed and less than the requested compressor speed. 7.A computer-program product comprising a non-transitory computer-usablemedium having computer-readable program code embodied therein, thecomputer-readable program code adapted to be executed to implement amethod comprising: receiving one of a heating-demand call and anend-defrost call; determining a requested compressor speed responsive tothe receiving step; comparing a requested compressor speed of avariable-speed compressor to a pre-defined threshold; responsive to adetermination that the requested compressor speed is greater than thepre-defined threshold, operating the variable-speed compressor at afirst compressor speed that is less than the requested compressor speed;wherein the operating step is performed for a pre-defined time period;and before expiration of the pre-defined time period, the comparing stepis repeated; responsive to a determination at the repeated comparingstep that the requested compressor speed is greater than the pre-definedthreshold, operating the variable-speed compressor at the firstcompressor speed that is less than the requested compressor speed. 8.The computer-program product of claim 7, the method comprising,responsive to a determination that the requested compressor speed is notgreater than the pre-defined threshold, operating the variable-speedcompressor at the requested compressor speed.
 9. The computer-programproduct of claim 7, the method comprising: responsive to a determinationat the repeated comparing step that the requested compressor speed isnot greater than the pre-defined threshold, operating the variable-speedcompressor at the requested compressor speed.
 10. The computer-programproduct of claim 7, wherein the method is performed on avapor-compression system.
 11. The computer-program product of claim 7,the method comprising: performing the operating step for a firstpre-defined time period; and after expiration of the first pre-definedtime period, operating the variable-speed compressor at a secondcompressor speed greater than the first compressor speed and less thanthe requested compressor speed.
 12. The computer-program product ofclaim 11, the method comprising, performing the step of operating thevariable-speed compressor at the second compressor speed for a secondpre-defined time period.
 13. The computer-program product of claim 12,the method comprising, after expiration of the second pre-defined timeperiod, operating the variable-speed compressor at a third compressorspeed greater than the second compressor speed and less than therequested compressor speed.
 14. A vapor-compression system comprising: avariable-speed compressor; an accumulator; a condenser; an evaporator;and a processor, wherein the processor is configured to: receive one ofa heating-demand call and an end-defrost call; determine a requestedcompressor speed responsive to the receiving step; compare a requestedcompressor speed of a variable-speed compressor to a pre- definedthreshold; responsive to a determination that the requested compressorspeed is not greater than the pre-defined threshold, operate, for apre-defined time period, the variable-speed compressor at the requestedcompressor speed; before expiration of the pre-defined time period,repeat the comparing step; responsive to a determination at the repeatedcomparing step that the requested compressor speed is greater than thepre-defined threshold, operate the variable-speed compressor at thefirst compressor speed that is less than the requested compressor speed;and responsive to a determination at the repeated comparing step thatthe requested compressor speed is not greater than the pre-definedthreshold, operate the variable-speed compressor at the requestedcompressor speed.
 15. The vapor-compression system of claim 14,comprising: a reversing valve; an expansion device; a condenser fan; andan evaporator fan.
 16. The vapor-compression system of claim 14, whereinthe processor is configured to: responsive to a determination that therequested compressor speed is greater than the pre-defined threshold,operating the variable-speed compressor at a first compressor speed thatis less than the requested compressor speed.
 17. The vapor-compressionsystem of claim 14, wherein the processor is configured to: perform theoperating step for a first pre-defined time period; and after expirationof the first pre-defined time period, operate the variable-speedcompressor at a second compressor speed greater than the firstcompressor speed and less than the requested compressor speed.
 18. Thevapor-compression system of claim 17, wherein the processor isconfigured to: perform the step of operating the variable-speedcompressor at the second compressor speed for a second pre-defined timeperiod; and after expiration of the second pre-defined time period,operate the variable-speed compressor at a third compressor speedgreater than the second compressor speed and less than the requestedcompressor speed.